Would Amazon have a business if everyone who bought something left and never bought something again? Would a restaurant ever succeed if no one ever came back? NO! There is only a finite amount of people in the world. Chances are, most of your business already comes from repeat customers. But how do you get more people coming back?
Hopefully you already know a bit about this. Obviously the most important thing is to treat your customers the way you would want to be treated in their shoes.
Think back to your last visits to a store or online store. Probably the only parts that stick in your mind are the really good and really bad parts.
More on this later, but start thinking about it.